An electro-tactile sense presenting apparatus (an electro-tactile display) is a tactile sense presenting apparatus for directly stimulating tactile nerves under the skin from electrodes on the skin. A basic electrical stimulation procedure using electrodes arranged in a two-dimensional matrix is shown in FIG. 2. Each electrode can be connected to a current source and to ground using two switches in a configuration known as a half-bridge circuit. By switching over these switches, each electrode may be made to operate as a current source (current source electrode) or ground (ground electrode). By making an electrode at a location for stimulate a current source and putting other electrodes to ground, a current path may be formed under the skin in a direction from a current source electrode to ground electrodes so that nerve axons are stimulated.
The case where the distance between electrodes is small is considered here. At this time, a current path formed below the skin is shallow because the distance between a current source electrode and the ground electrodes is short. A problem therefore occurs where nerve axons that are at deep sections cannot be sufficiently stimulated. Specifically, in the case of the skin of a fingertip, human tactile resolution is in the order of 1.5 mm and it is therefore wished to arrange electrodes at approximately 1.5 mm. However, an appropriate distance between the current source electrode and ground electrode in order to stimulate nerves underneath the skin is about 2 to 3 mm. The problem described above is therefore extremely important.
If, at the switching circuit of FIG. 2, a high-impedance mode (a state where the two switches are both open) is possible, by taking electrodes neighboring the current source electrode to be high-impedance electrodes and taking electrodes at locations a little further away to be ground electrodes, it becomes possible to broaden the distance between the current source and ground and this problem no longer occurs (right side of FIG. 3). In non-patent document 1, a switching circuit is disclosed that provides a high-impedance mode where the two switches are open, and a short-circuit mode where the two switches are closed.
Here, when actually designing a device incorporating the above system, it is necessary to use an integrated circuit having a large number of half-bridge circuits in order to miniaturize the switching circuit portion. However, half-bridge circuits adopted in integrated circuits compatible with high-voltages do not have the high-impedance mode and short-circuit mode. It should also be considered that the main application of a high-voltage half-bridge circuit is to control micro-machines. In this application, these modes are not only unnecessary, but may also be harmful. Integrated circuits that are actually utilized do not have the high-impedance mode and this method therefore cannot be used for solving the problem.
Non-patent document 1: Takahashi, Kajimoto, Kawakami, Tachi, “Electro Tactile Display with Localized High-Speed Switching”, Proceedings of the Virtual Reality Society of Japan Seventh Annual Conference (Tokyo, September 2002), pp. 145-148, 2002.
It is therefore an object of the present invention to stimulate nerve axons of deep sections in a superior manner in electrical stimulation using an array of electrodes without deteriorating spatial resolution of the tactile stimulation even in cases where interval between the electrodes is narrow.